The invention relates to hybrid resins that constitute a system of discrete weak acid and weak base resin particles. The hybrid resins comprise a macroporous copolymer, termed the “host”, which is at least partially filled in its macropores with a cross-linked copolymer of a different nature, termed the “guest”. Thus there is a location of one type of polymer in the pores and another type of polymer in the framework of the hybrid resin.
The term “hybrid” indicates that the resins have some of the characteristics or properties of both a gel and a macroporous copolymer, but also that they have distinct properties of their own. The pores of the macroporous host copolymer may be filled with the guest copolymer utilizing varying percentages of crosslinking agent by introducing the guest copolymer or the guest copolymer-forming monomer components in varying amounts. The resins may also be prepared by filling the pores of the macroporous host copolymer with additional macroreticular copolymers in varying amounts with varying crosslinker contents or varying amounts of phase extender.
The host copolymer possesses a porous structure referred to as macroporous, which means it possesses a network of microscopic channels extended through the mass. While small, these channels are large in comparison with pores in a gel that are not visible, for example, in electronic photomicrographs. A typical macroporous (MP) copolymer has a surface area of at least about 1 m2/gm and pores larger than about 50-20 Å. Usually the MP copolymers are produced in bead form having a particle size of around 10-900 microns. Similar types of monomeric materials are used in preparing the MP host copolymer and the guest copolymer, but the preparation process is varied to impart different characteristics such as porosity to the different phases of the hybrid resins.
As used herein, the term “elution” refers to the removal of ions, both cations and anions, which have been loaded onto the resin during the absorption process. The term “regeneration” refers to restoration of the functional groups to the resin to the zwitterion form. These operations are each thermally activated and essentially simultaneously occur. Therefore, elution will necessarily also involve regeneration.